Capacitive detection type electro-mechanical transducer

ABSTRACT

A capacitive detection type electro-mechanical transducer comprises; a cell formed by a first electrode arranged on a substrate and a second electrode arranged on a vibration film, and a detection circuit for detecting a displacement of the vibration film, based on a capacity change between the first and second electrodes, wherein a plurality of the cells are classified into a plurality of groups, each one includes at least two cells, and the first electrodes or the second electrodes of the cells of the same one group are commonly connected to the same one detection circuit, and an addition circuit for adding, into single information, signals from the plurality of detection circuits corresponding to the plurality of groups, and for outputting the information, and a capacitive load for each one of the detectors are formulated to be dispersedly arranged.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a capacitive detection typeelectro-mechanical transducer, and specifically relates to a capacitivedetection type electro-mechanical transducer that can be employed for,e.g., a capacitive detection type ultrasonic sensor.

2. Description of the Related Art

There are known diagnostic apparatuses for breast tumors, which applythe photoacoustic effect.

For example, in order to detect ultrasonic waves from an object, a PVDFsensor (approximately 75 mm square) including a total of 590 pixelsarranged with a pitch of approximately 3 mm, each pixel having a widthof 2 mm is used. PVDF sensors have a wider bandwidth compared to PZTsensors.

As with PVDF sensors, capacitive detection type ultrasonic sensors(CMUTs: Capacitive Micromachined Ultrasonic Transducers) using a MEMStechnique have been proposed as sensors having a wider bandwidthcompared to PZT sensors (A. S. Ergun, Y. Huang, X. Zhuang, O. Oralkan,G. G. Yaralioglu, and B. T. Khuri-Yakub, “Capacitive micromachinedultrasonic transducers: fabrication technology”, IEEE Transactions onUltrasonics, Ferroelectrics, and Frequency Control, Vol. 52, No. 12,p.p. 2242-2258, Dec. 2005).

CMUTs can be formed at low cost because they are formed by applying asemiconductor process. For CMUTs, a pixel pitch of 250 to 400 μm is useddepending on the frequency band of the object to be measured.

It can be expected that use of a CMUT in a breast tumor diagnosticapparatus applying the photoacoustic effect brings cost reduction in thesensor part of the apparatus.

However, as a result of diligent study, the present inventors found thatif the pixel size of a CMUT is simply increased (i.e., the number ofcells (or elements) included in one pixel is increased), the followingproblems arise.

A CMUT, which is an electrostatic capacitive detection type sensor,includes a detection circuit that detects a current change caused by acapacitance change.

If a pixel size employed for a conventional CMUT is increased to a sizefor a breast tumor diagnostic apparatus, a larger capacitance load willbe put on each pixel in the CMUT. Thus, a larger load will be put oneach detection circuit, causing a problem in requiring the detectionbandwidth to be narrowed in order for the detection circuit to stablyoperate.

In view of the above problem, an object of the present invention is toprovide a capacitive detection type electro-mechanical transducerenabling expansion of a frequency bandwidth for each detection circuitto stably operate, and thus, enabling provision of a wide detectionbandwidth even where the size of each pixel is increased.

SUMMARY OF THE INVENTION

A capacitive detection type electro-mechanical transducer according tothe present invention comprises a cell formed by a first electrodearranged on a substrate and a second electrode arranged on a vibrationfilm in opposition to the first electrode to form a gap between thefirst and second electrodes; and a detection circuit for detecting adisplacement of the vibration film, based on a capacity change betweenthe first and second electrodes, wherein a plurality of the cells areprovided, and a plurality of detection circuits are provided, theplurality of cells are classified into a plurality of groups, each oneincludes at least two cells, and the first electrodes or the secondelectrodes of the cells of the same one group are commonly connected tothe same one detection circuit, and an addition circuit for adding, intosingle information, signals from the plurality of detection circuitscorresponding to the plurality of groups, and for outputting theinformation, and a capacitive load for each one of the detectors areformulated to be dispersedly arranged.

The present invention achieves a capacitive detection typeelectro-mechanical transducer enabling expansion of a frequencybandwidth for each detection circuit to stably operate, and thus,achieves a wide detection bandwidth even where the size of each pixel isincreased.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a capacitive detection typeelectro-mechanical transducer according to a first embodiment.

FIG. 2 is a diagram illustrating a capacitive detection typeelectro-mechanical transducer according to a second embodiment.

FIG. 3 is a diagram illustrating a capacitive detection typeelectro-mechanical transducer according to a third embodiment.

FIG. 4 is a diagram illustrating a capacitive detection typeelectro-mechanical transducer according to a fourth embodiment.

FIG. 5 is a diagram illustrating a capacitive detection typeelectro-mechanical transducer according to a fifth embodiment.

FIG. 6 is a diagram illustrating a capacitive detection typeelectro-mechanical transducer according to a sixth embodiment.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

Hereinafter, an example of a configuration of a capacitive detectiontype electro-mechanical transducer according to each of embodiments ofthe present invention, which is capable of detecting a displacement of avibration film based on a capacitance change between a first electrode(detection electrode) and a second electrode (bias electrode) will bedescribed with reference to the drawings. In the present invention, thefirst electrode and the second electrode may be arranged with a gaptherebetween. For the functions of the respective electrodes, the firstelectrode may be a bias electrode while the second electrode being adetection electrode. In other words, in the present invention, eitherthe first electrode or the second electrode may be used as a detectionelectrode.

First Embodiment

A CMUT forming a capacitive detection type electro-mechanical transduceraccording to a first embodiment will be described with reference to FIG.1.

In the CMUT according to the present embodiment, one pixel refers to anarea in which ultrasonic wave information received by a vibration film101 is output as one piece of averaged information.

In one pixel 1, amplitude and phase information for ultrasonic waves isaveraged, and the relevant apparatus forms an image of an object basedon the pixel-based amplitude and phase information.

The vibration film 101 is supported by a supporting portion 103 formedon a substrate 106. Each of the vibration film 101, the supportingportion 103 and the substrate 106 includes an insulating material.

The CMUT according to the present embodiment includes detectionelectrodes (first electrodes) 105 arranged on the substrate 106, andbias electrodes (second electrodes) 102 arranged on the vibration films101 via the detection electrodes 105 and gaps 104 so as to face thedetection electrodes 105.

A configuration set including a detection electrode arranged on asubstrate and a bias electrode arranged on a vibration film via thedetection electrode and a gap so as to face the detection electrode isreferred to as a “cell”.

A constant DC voltage is applied to each bias electrode 102. Thepressure of each gap 104 portion is reduced by the pressure of theatmosphere.

Each vibration film 101 bends to the substrate 106 side owing to anelectrostatic force generated by the difference in potential between thebias electrode 102 to which a bias voltage has been applied and thedetection electrode 105, and the difference between the pressure of theatmosphere applied to the upper portion of the vibration film 101 andthe pressure of the gap 104 portion.

Upon the vibration film 101 vibrating according to ultrasonic waves, anelectrostatic capacitance between the bias electrode and the detectionelectrode changes according to the vibration.

The electrostatic capacitance change and the bias voltage applied to thebias electrode cause the detection electrode 105 to generate aninductive charge, resulting in a weak current flowing in the detectionelectrode 105.

The CMUT according to the present embodiment includes a plurality ofcells in each pixel.

The size (thickness and diameter) of a vibration film in each cell isdetermined so that the vibration film can easily vibrate at thefrequencies of detection-target ultrasonic waves. The size of each pixelis determined by the wavelengths of detection-target ultrasonic waves.

In general, the cell has a diameter in a range of around ten to severaltens of micrometers, and as mentioned in the Description of the RelatedArt section above, each pixel has a size of around 2 mm in a breasttumor diagnostic apparatus applying the photoacoustic effect.

Therefore, each pixel includes a plurality of (around 100 to 4000 in theabove example) cells.

In the CMUT according to the present embodiment, the cells in each pixelare divided into N groups.

More specifically, each pixel includes a plurality of groups, eachincluding detection electrodes (first electrodes) 105 interconnected viaa wiring and further connected to a same detection circuit 107.

Although FIG. 1 illustrates an example in which the electrodes 105arranged on the substrate 106 are used for the first electrodes, whichare detection electrodes, in the present invention, the first electrodes105 and the second electrodes 102, which are bias electrodes, may beinterchanged to use the second electrodes for the detection electrodes.In this case, each pixel may include a plurality of groups, eachincluding detection electrodes (second electrodes) 102 interconnectedvia a wiring and further connected to a same detection circuit 107.

The CMUT according to the present invention includes one detectioncircuit for each of N groups (N detection circuits in total) in eachpixel.

Consequently, a capacitance load imposed on each detection circuit canbe dispersed, enabling expansion of a frequency bandwidth for detectionsignals in which the detection circuit stably operates, and thus,enabling provision of a CMUT that can provide a wide bandwidth to abreast tumor diagnostic apparatus applying the photoacoustic effectwithout narrowing the detection bandwidth even though the pixel size isincreased.

The CMUT according to the present embodiment includes one additioncircuit 108 for each pixel.

Each addition circuit 108 adds up all the output signals from the Ndetection circuits included in the relevant pixel and outputs a signalresulting from the addition to an output signal terminal of the CMUT.

Provision of an addition circuit 108 for each pixel enables reduction ofthe number of wirings drawn to the outside of the CMUT.

Consequently, downsizing and reliability enhancement of the CMUT can beachieved. Also, a load on an apparatus that receives signals from theCMUT can be reduced.

Second Embodiment

A CMUT forming a capacitive detection type electro-mechanical transduceraccording to a second embodiment will be described with reference toFIG. 2.

FIG. 2 is a diagram of a configuration of a trans-impedance circuit.

The configuration in FIG. 2 includes an operational amplifier 201,resistances 202 and 204 and capacitors 203 and 205. Componentscorresponding to those in FIG. 1 will be described with reference toFIG. 1.

The present embodiment is the same as the first embodiment except theconfiguration of each detection circuit and the division count relatedthereto. Here, a detection circuit 107 is a circuit for detecting a weakcurrent generated by vibration of a vibration film.

In the present embodiment, a trans-impedance circuit, which is acurrent-to-voltage conversion circuit that converts a change in a weakcurrent into a voltage, is used.

In FIG. 2, the operational amplifier 201 is connected to positive andnegative power supplies VDD and VSS.

An inverting input terminal (−IN) of the operational amplifier 201 isconnected to a wiring from a detection electrode 105 in the CMUT.

An output terminal (OUT) of the operational amplifier 201 is connectedto the inverting input terminal (−IN) via the resistance 202 and thecapacitor 203 connected in parallel, forming a configuration in which anoutput signal is fed back.

A non-inverting input terminal (+IN) of the operational amplifier 201 isconnected to a ground terminal (GND) via the resistance 204 and thecapacitor 205 connected in parallel.

The voltage of the ground terminal (GND) has an intermediate potentialbetween the positive power supply VDD and the negative power supply VSS.

The resistances 202 and 204 has a same resistance value and thecapacitors 203 and 205 have a same capacitance value.

Each detection circuit 107 according to the present embodiment convertschanges in currents from corresponding detection electrodes 105 into avoltage value according to the current changes by means of atrans-impedance circuit and outputs the voltage value.

The trans-impedance circuit has a wide bandwidth compared to othercircuit configurations.

Furthermore, since an output signal from the detection circuit 107 takesthe form of a voltage value, signal degradation is less likely to occurin a wiring connected to an addition circuit.

Each addition circuit 108 is a voltage addition circuit, which adds upoutput voltages from corresponding detection circuits 107 and outputsthe resulting voltage from an output terminal to the outside.

Here, it is assumed that a gain bandwidth of the operational amplifier201 is GBW, the resistance values of the resistances 202 and 204 are RF,the capacitance values of the capacitors are CF, and a capacitanceparasitic in the non-inverting input terminal (+IN) of the operationalamplifier is Cin.

When an operational amplifier is made to perform a trans-impedanceoperation in the trans-impedance circuit illustrated in FIG. 2, it isnecessary to consider the stability of the overall circuit because aninput signal is subjected to a negative feedback via RF and CF. Wherethe capacitance Cin parasitic in the input terminal is large, thenegative feedback circuit becomes unstable, which may result in thecircuit itself oscillating. When the circuit has entered such state, thecircuit cannot perform current-to-voltage conversion that it shouldperform, and thus, it is necessary to select optimum GBW, RF and CFconsidering the circuit stability for the value of Cin.

When the input terminal has the parasitic capacitance Cin, it isnecessary to satisfy expression (1) in order for the operationalamplifier to stably operate.

Cin≦π×GBW×R _(F)×(C _(F))²  Expression (1)

It is assumed that a capacitance parasitic in the detection electrode105 portions is Cmut for one pixel in the CMUT. It is also assumed thata parasitic capacitance is Cwiring for one wiring connected from thedetection electrodes 105 to the detection circuit 107. Furthermore, itis assumed that a division count for one pixel, that is, the number ofgroups in which detection electrodes are connected (the number ofdetection circuits) is an integer N.

The parasitic capacitance Cin of the input terminal can be expressed byexpression (2) using the capacitance Cmut parasitic in the detectionelectrode 105 portions and the capacitance Cwiring parasitic in theconnection wiring, and the division count N for one pixel.

$\begin{matrix}{{Cin} = {\frac{Cmut}{N} + {Cwire}}} & {{Expression}\mspace{14mu} (2)}\end{matrix}$

Expression (3) can be derived from expressions (1) and (2).

$\begin{matrix}{N \geq \frac{Cmut}{{\pi \times {GBW} \times R_{F} \times \left( C_{F} \right)^{2}} - {Cwire}}} & {{Expression}\mspace{14mu} (3)}\end{matrix}$

Determining the division count N so as to satisfy expression (3) enablesa stable circuit operation even using a predetermined constant for thetrans-impedance circuit.

In the CMUT according to the present embodiment, the division count Nfor one pixel is determined using expression (3).

As described above, the division count N and the detection circuit countcan be determined in relation to the gain bandwidth of an operationalamplifier, the parasitic capacitance generated in the detectionelectrodes forming the detection electrodes for one piece ofinformation, and the parasitic capacitance between the detectionelectrodes and the corresponding detection circuit, based on thepredetermined gain bandwidth, the feedback capacitance and theresistance value of the trans-impedance circuit.

Consequently, with detection circuits, the number of which is set to N,even where the pixel size is increased, the detection circuits can bemade to stably operate for a wide bandwidth.

Third Embodiment

A CMUT forming a capacitive detection type electro-mechanical transduceraccording to a third embodiment will be described with reference to FIG.3.

The present embodiment is the same as the first and second embodimentsexcept the configurations of detection circuits and addition circuits.

The configuration illustrated in FIG. 3 includes current amplificationcircuits 301, a current addition circuit 302 and a current-to-voltageconversion circuit 303. Detection circuits 107 are formed by the currentamplification circuits 301.

Also, an addition circuit 108 is formed by the current addition circuit302 and the current-to-voltage conversion circuit 303.

Each current amplification circuit 301 amplifies a weak current from thecorresponding detection circuit 107, performs impedance conversion andoutputs the resulting current to the addition circuit 108.

In the addition circuit 108, a plurality of input currents are added upby means of the current addition circuit 302.

A current resulting from the addition is converted into a correspondingvoltage signal in the current-to-voltage conversion circuit, and outputto the outside of the CMUT.

The current amplification circuits 301 and the current addition circuit302 can be provided in a smaller circuit area compared to thetrans-impedance circuit and the voltage addition circuit used in thefirst embodiment. Accordingly, the areas of the detection circuit 107and the addition circuit 108 can be decreased.

Use of the CMUT according to the present embodiment enables provision ofa CMUT with a smaller circuit area without narrowing the detectionbandwidth even where the pixel size is increased.

Fourth Embodiment

A CMUT forming a capacitive detection type electro-mechanical transduceraccording to a fourth embodiment will be described with reference toFIG. 4.

The present embodiment is the same as the first to third embodimentsexcepts the configuration of substrates on which detection circuits andaddition circuits are formed.

FIG. 4 is a diagram illustrating a configuration of the CMUT accordingto the present embodiment.

The configuration illustrated in FIG. 4 includes a first substrate 401,a second substrate 402, penetrating wirings 403, detection circuitoutput terminals 404, addition circuit input terminals 405 and bumps406.

On a surface of the first substrate 401, cells in a plurality of groupsare arranged with the respective detection electrode sides (firstelectrode sides) of the cells facing the surface.

In other words, on one surface of the substrate, pixels, each includingcells that each includes a detection electrode 105, are formed.

Also, on another surface of the substrate (surface opposite the surfaceon which the cells in the plurality of groups are provided), respectivedetection circuits in the plurality of groups are formed. In otherwords, N detection circuits 107 are formed for each pixel.

The first substrate 401 includes a number of wirings penetrating thesubstrate, the number corresponding to a pixel count P multiplied by thecell count for one pixel, and detection electrodes for each group areconnected to a corresponding detection circuit (PxN detection circuitsin the entire CMUT) via the corresponding penetrating wirings.

On the second substrate 402, a number of addition circuits, the numbercorresponding to the pixel count P, are formed.

Output terminals of the detection circuits formed on the first substrate401 and input terminals 405 of the addition circuits formed on thesecond substrate are electrically connected by pixel via bumps.

Output signals from the CMUT are drawn out to a number of terminalsformed on the second substrate 402, the number corresponding to thepixel count P, via a number of wirings, the number corresponding to thepixel count.

Using the CMUT according to the present embodiment, the length of eachwiring from pixels can be suppressed to around the thickness of thefirst substrate 401, enables reduction of parasitic capacitancesgenerated by the wirings.

Accordingly, a wide bandwidth CMUT with a further decreased load on thedetection circuits.

Fifth Embodiment

A CMUT forming a capacitive detection type electro-mechanical transduceraccording to a fifth embodiment will be described with reference to FIG.5.

The present embodiment is the same as the fourth embodiment except thepositions on a substrate where detection circuits are formed.

On a first substrate 401, detection circuits 107 are formed, and pixels,each including cells that each include a detection electrode 105, arefurther formed on these detection circuits.

The first substrate 401 includes a number of wirings penetrating thesubstrate, the number corresponding to a pixel count multiplied by N. Anoutput terminal of a detection circuit provided for each group (P×Ndetection circuits in the entire CMUT) is connected to a correspondingelectrode 407 on another side via the corresponding penetrating wiring.On a second substrate 402, a number of addition circuits, the numbercorresponding to the pixel count P, are formed.

The electrodes 407 on the first substrate 401 and input terminals 405 ofthe addition circuits formed on the second substrate 402 areelectrically connected by pixel via bumps.

Output signals from the CMUT are drawn out to a plurality of terminals,the number corresponding to the pixel count P, via a number of wiringsformed on the second substrate 402, the number corresponding to thepixel count.

By using the CMUT according to the present embodiment, the length ofeach wiring from the pixels can be minimized, enabling substantialreduction of parasitic capacitances caused by the wirings. Furthermore,the number of penetrating wirings can be reduced compared to that of thefifth embodiment. Accordingly, a sensor with a wider bandwidth, whichenables further reduction of a load on the detection circuits, can beprovided. In addition, the reliability of the sensor can be enhanced.

Sixth Embodiment

A CMUT forming a capacitive detection type electro-mechanical transduceraccording to a sixth embodiment will be described with reference to FIG.6.

The present embodiment is the same as the first to third embodimentsexcept the positions where detection circuits and addition circuits areformed.

On a substrate 401, N detection circuits 107 and one addition circuit108 are formed within an area corresponding to one pixel. On thesecircuits, pixels, each including cells that each include a detectionelectrode 105, are formed in a two-dimensional array.

Output signals from the CMUT are drawn out to a number of terminals, thenumber corresponding to a pixel count (P), via a number of wiringsformed on the substrate 401, the number corresponding the pixel count.

By using the CMUT according to the present embodiment, the length ofeach wiring from the pixels can be minimized, enabling substantialreduction of parasitic capacitances caused by the wirings. Accordingly,a sensor with a wider bandwidth, which enables further reduction of aload on the detection circuits, can be provided.

In addition, the length of each wiring between the detection circuitsand the addition circuits can be minimized, and thus, signal degradationcaused before addition of outputs from the detection circuits can besuppressed, enabling provision of a high-performance CMUT with reducedsignal degradation.

Since the configuration of the present embodiment requires arranging aplurality of detection circuits and one addition circuit in each pixel,it is more effective to use the present embodiment in combination of thethird embodiment that can suppress the circuit area.

Also, in the third embodiment, current signals are used fortransportation from the detection circuits to the addition circuits, andthus, it is highly likely that an increase in length of the wirings mayresult in noise application and signal degradation, compared to a methodusing voltages for transportation.

With the present embodiment, the wirings from the detection circuits tothe addition circuits can be minimized, and thus, a combination of thepresent embodiment and the third embodiment enables provision of ahigh-performance CMUT with further reduced signal degradation.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2010-003649, filed Jan. 12, 2010, which is hereby incorporated byreference herein in its entirety.

1.-6. (canceled)
 7. A capacitive detection type electro-mechanicaltransducer comprising: a plurality of cells, each cell including a firstelectrode, and a second electrode opposed to the first electrode with agap between the first and second electrodes, and configured to vibrate,a plurality of detection circuits, each detection circuit beingconfigured to detect a current output from a detection electrode that isone of the first and second electrodes; and an addition circuit foradding signals from the plurality of detection circuits wherein theplurality of cells are classified into a plurality of groups, each groupincludes at least two cells, wherein a plurality of the detectionelectrodes of the cells in one group are commonly connected to onedetection circuit, and wherein each of the plurality of detectioncircuits comprises a current-to-voltage conversion circuit that convertscurrents output from the plurality of the detection electrodes of thecells in one group into a voltage.
 8. The capacitive detection typeelectro-mechanical transducer according to claim 7, wherein thedetection circuit comprises a trans-impedance circuit including anoperational amplifier, and the addition circuit comprises a voltageaddition circuit, such that, based on a predetermined frequency of thedetection circuit, a predetermined feedback capacitance or resistancevalue of the trans-impedance circuit, to a gain band width of theoperational amplifier, a parasitic capacitance in the detectionelectrodes connected to the one detection circuit, and a parasiticcapacitance in a wiring between the detection electrodes and thedetection circuit, a number of the plurality of detection circuits isdetermined.
 9. The capacitive detection type electro-mechanicaltransducer according to claim 7, further comprising: a first substrateprovided such that the plurality of groups of the cells are arranged onone side of the first substrate, the detection circuits are arranged onthe other side of the first substrate opposite to the one side, and asecond substrate provided such that the addition circuit is arranged onthe second substrate, wherein the detection electrode is connected to aninput terminal of the detection circuit through a wiring penetrating thefirst substrate, and wherein an output terminal of the detection circuitis connected through a bump to an input terminal of the additioncircuit.
 10. The capacitive detection type electro-mechanical transduceraccording to claim 7, further comprising; a first substrate providedsuch that the detection circuits are arranged on one side of the firstsubstrate, and a second substrate provided such that the additioncircuit is arranged on the second substrate, and wherein the pluralityof groups of the cells are arranged on the detection circuitscorresponding thereto so that the first electrode of the cell isarranged in opposition to the detection circuit, wherein an outputterminal of the detection circuit is connected through a wiringpenetrating the first substrate to an electrode arranged on the otherside of the first substrate opposite to the one side, and wherein aninput terminal of the addition circuit is connected through a bump tothe electrode arranged on the other side of the first substrate.
 11. Thecapacitive detection type electro-mechanical transducer according toclaim 7, further comprising; a first substrate provided such that thedetection circuits and the addition circuit are arranged on one side ofthe first substrate, wherein the plurality of groups of the cells arearranged two dimensionally on the detection circuits and the additioncircuit, wherein and the first electrode of the cell is arranged inopposition to the detection circuit and the addition circuit.
 12. Thecapacitive detection type electro-mechanical transducer according toclaim 7, wherein the cell comprises a vibration film on which the secondelectrode is arranged.
 13. The capacitive detection typeelectro-mechanical transducer according to claim 7, wherein the otherelectrode of the first and second electrodes is bias electrode to whicha bias voltage is applied.
 14. The capacitive detection typeelectro-mechanical transducer according to claim 7, wherein the cellreceives an ultrasonic wave, and wherein an output from the additioncircuit corresponds to information of the received ultrasonic wave inone pixel.